This publication provides the GAEZ v4 model documentation for: (1) Agro-climatic analysis; (2) Crop biomass and yield calculations; (3) Land Utilization Types; and (4) Observed phenology and crop calendars; (5) Temperature sum and temperature profile constraint-factors; (6) Crop-specific water requirements; (7) Soil-water balance; (8) Agro-climatic constraints; (9) Agro-edaphic constraints more crops; (10) Agro-ecological crop potentials; (11) Actual crop production and yields; and (12) Yield and production gaps. This GAEZ v4 model documentation summarizes information on the structure of GAEZ methodology and provides information on updates of input data and model procedures from GAEZ v3.